The present invention relates to hermetic compressors and more particularly to two stage compressors using carbon dioxide as the working fluid.
Conventionally, multi-stage compressors are ones in which the compression of the refrigerant fluid from a low, suction pressure to a high, discharge pressure is accomplished in more than one compression process. The types of refrigerant generally used in refrigeration and air conditioning equipment include clorofluorocarbons (CFCs) and hydrochlorofluorocarbon (HCFC). Additionally, carbon dioxide may be used as the working fluid in refrigeration and air conditioning systems. By using carbon dioxide refrigerant, ozone depletion and global warming are nearly eliminated. Further, carbon dioxide is non-toxic, non-flammable, and has better heat transfer properties than CFCs and HCFC, for example. The cost of carbon dioxide is significantly lower than CFC and HCFC. Additionally, it is not necessary to recover or recycle carbon dioxide which contributes to significant savings in training and equipment.
In a two stage compressor, the suction pressure gas is first compressed to an intermediate pressure. The intermediate pressure gas can be directed to the second stage suction side or cooled in the unit heat exchanger before delivery to the second stage suction. The intermediate pressure gas is next drawn into a second compressor mechanism where it is compressed to a higher, discharge pressure for use in the remainder of a refrigeration system.
The compression mechanisms of the two stage compressor may be stacked atop one another on one side of the motor, or positioned with one located on each side of the motor. When the compression mechanisms are located adjacent one another, on one side of the motor, problems may occur. Such problems include overheating of the suction gas supplied to the first stage compression mechanism which affects volumetric efficiency of the compressor performance. Heat transfer from the discharge pressure pipe heats the suction pressure gas due to the close proximity of the pipes. Additional reduction of the compressor efficiency and possible reliability problems may be created by the overheating due to the closeness of the pumps of the compression mechanisms.
Further, in general, the compressor motor is located within the compressor housing and is surrounded by suction pressure gas which helps to cool the motor during compressor operation. The suction pressure gas is then supplied to the second stage compression mechanism along with the intermediate pressure compressed gas from the first stage compression mechanism. If the suction pressure gas is overheated, the gas surrounding the electric motor and entering the second stage compression mechanism may not be sufficiently cooled.
The compression mechanisms may further have parallel compression operation in which the suction gas is drawn into both compression mechanisms simultaneously. If, for example, alternative refrigerants are used and the compression mechanisms are in a parallel configuration, the compression mechanisms may be unable to withstand the high operating pressure experienced with compression of some of these refrigerants such as carbon dioxide.
A further potential problem with prior art compressors is the use of CFCs and HCFC refrigerants. These refrigerants may contribute to global warming and ozone depletion.
It is desired to provide a two stage hermetic compressor which uses carbon dioxide as the working fluid and provides the motor and compression mechanisms with separate housings to eliminate overheating.
The present invention relates to a two stage hermetic compressor which uses carbon dioxide as the working fluid. The compressor has a pair of compression mechanisms located at opposite ends of an electric motor. The compression mechanisms and motor are housed in separate housings forming modules which are secured to one another. A drive shaft operatively connects the motor and compression mechanisms. Low pressure carbon dioxide gas is supplied to the lower compression module in a first stage. The gas is compressed to an intermediate pressure and is discharge to a unit cooler located out side the compressor housing. The intermediate pressure, cooled refrigerant gas is introduced into a cavity located within the electric motor module. The intermediate pressure gas then exits the intermediate pressure cavity and enters the upper compression mechanism module through a suction port for the second stage compression. A conical baffle is affixed to the upper compression mechanism housing, extending into the motor housing, to protect the suction port of the upper compression mechanism from direct suction of oil. The intermediate refrigerant gas is compressed in the upper compression mechanism from an intermediate pressure to a high pressure and is discharged from the upper compression module into a cavity defined in the module. The discharge pressure gas is then exhausted from the compressor housing to the refrigeration system.
The present invention provides a two stage hermetic compressor for compressing carbon dioxide refrigerant received therein substantially at a suction pressure and discharged therefrom substantially at a discharge pressure. The compressor includes a housing having at least two cavities with one of the cavities containing discharge pressure carbon dioxide gas and one of the cavities containing carbon dioxide gas at a pressure intermediate the suction and discharge pressures. A first compression mechanism is located in the housing to compress suction pressure gas to a pressure intermediate the suction and discharge pressures. A motor is located in the intermediate pressure gas cavity. A second compression mechanism is located in the discharge pressure gas cavity where the gas at a pressure intermediate the suction and discharge pressures is compressed to discharge pressure. A drive shaft operatively couples the motor and the first and second compression mechanisms.
The present invention also provides a two stage hermetic compressor for compressing carbon dioxide refrigerant received therein including a first module having a motor mounted therein. The first module has first and second ends. A second module having a compression mechanism mounted therein is mounted to the first end of the first module. The motor and the second module compression mechanism are operatively coupled via a drive shaft. A third module having a compression mechanism mounted therein is mounted to the second end of the first module. The motor and the third module compression mechanism are operatively coupled by the drive shaft.
The present invention further provides a two stage hermetic compressor for compressing carbon dioxide refrigerant therein including a housing having at least two cavities. A motor is mounted in a first of the two cavities and a compression mechanism is mounted in a second of the two cavities. The motor is operatively coupled to the compression mechanism via a drive shaft. A port is located between the motor and the compression mechanism cavities through which carbon dioxide gas in the first cavity enters the second cavity. A baffle is mounted over the port to separate oil entrained in the carbon dioxide gas received in the motor cavity therefrom. The oil is prevented from entering the port.
The present invention provides a method of compressing carbon dioxide refrigerant gas from a suction pressure to a discharge pressure in a two stage hermetic compressor including drawing carbon dioxide refrigerant gas substantially at suction pressure into a first module having a compression mechanism mounted therein; compressing the carbon dioxide refrigerant gas to a pressure intermediate the suction and discharge pressures; cooling the carbon dioxide refrigerant gas at a pressure intermediate the suction and discharge pressures, collecting the intermediate pressure refrigerant gas in a second module having a motor mounted therein; drawing the intermediate pressure carbon dioxide refrigerant gas from the second module into a compression mechanism mounted in a third module; separating oil entrained in the intermediate pressure refrigerant gas therefrom by a baffle mounted between the second and third modules; compressing the intermediate pressure carbon dioxide refrigerant gas to a discharge pressure and discharging the discharge pressure refrigerant gas into the third module; and discharging the high pressure carbon dioxide refrigerant to a refrigeration system.
One advantage of the present invention is the location of the compression mechanisms at opposite ends of the motor which significantly reduces the heat transfer between the first and second stage compression mechanisms and input passages.
An additional advantage of the present invention is the modular design. The motor and compression mechanisms are provided with having individual housings with the motor module remaining at substantially intermediate pressure and the second stage compression mechanism module being at substantially discharge pressure. The modular design also reduces the cost of assembly of the compressor.
Another advantage of the present invention is that the gas compressed in the first stage compression mechanism is cooled before entering the motor module which prevents overheating of the motor.